This research will provide data on culture requirements for supporting normal growth of hamster preimplantation embryos in vitro. Embryos at all stages of preimplantation development will be cultured in a relatively simple medium, which will be progressively modified as important rate-limiting parameters for embryo growth are defined. Parameters to be examined include physicochemical conditions and nutrients. Embryo growth will be evaluated by several qualitative criteria, including transfer of cultured embryos to pseudopregnant recipients to assess their normality. The primary purpose of this study is to determine which features of the environment are critically important for normal embryo growth and differentiation. The information obtained in this study will also be applied to embryos from cattle and rhesus monkeys to test the general applicability of the data. Steroid metabolic pathways in cultured hamster embryos will also be examined since steroids seem to exercise important regulatory actions on embryo growth and differentiation. The final part of the research will make use of our ability to obtain normal preimplantation growth of hamster embryos in vitro to examine consequences of delayed fertilization on subsequent embryogenesis. Overall, the research will provide data on the regulation of normal preimplantation embryo development by environmental conditions; this information is likely to be helpful in understanding some of the regulatory events involved in normal human development and in anomalous embryogenesis, including pregnancy losses and developmental defects. The data are also likely to assist efforts aimed at improving the efficiency of in vitro fertilization and embryo culture/transfer as therapeutic procedures for human infertility.